I have a Sansui QA-7000 4 channel amplifier. There is a BTL circuit so it can be bridged to 2 channels.
The preamp can be separated so a 1kHz sinewave is input at the main in inputs. If there is no load the the signal looks ok but with a load at the speaker terminals, the signal “soft clips”.
The bias is correct and stable.
When the driver boards are swapped the problem stays on the left channel
The voltages are correct at the transistors of the BTL board and the voltages at the driver boards seem correct.
Pictures are Left and Right channels with load and with no load.
The preamp can be separated so a 1kHz sinewave is input at the main in inputs. If there is no load the the signal looks ok but with a load at the speaker terminals, the signal “soft clips”.
The bias is correct and stable.
When the driver boards are swapped the problem stays on the left channel
The voltages are correct at the transistors of the BTL board and the voltages at the driver boards seem correct.
Pictures are Left and Right channels with load and with no load.
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Hi,
My advice since you have an scope is to start scoping from the input to the the final drivers. Since the distortion it is in the negative side I would scope the negative circuit to see where the signal start to get distorted.
My advice since you have an scope is to start scoping from the input to the the final drivers. Since the distortion it is in the negative side I would scope the negative circuit to see where the signal start to get distorted.
This is not going to help, as in the feedback amplifier, distortion will be visible everywhere within the loop.
Stonehome - did you check those fuses (F1 - F4)?
It looks like one of the output transistors' emitters is disconnected - with no load, the negative half of the sine wave is formed by the driver stage. As soon as the load is in place, the driver stage is not able to provide enough current , so the output sine wave clips.
Stonehome - did you check those fuses (F1 - F4)?
It looks like one of the output transistors' emitters is disconnected - with no load, the negative half of the sine wave is formed by the driver stage. As soon as the load is in place, the driver stage is not able to provide enough current , so the output sine wave clips.
Thanks Valery, the fuses are ok but I'll check the output emitter more closely. Thanks.
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Cool ) It would also make sense to check the outputs, at least to make sure they are not shorted (c-e), before you power it on with the fuses replaced.
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